1. Field of the Invention
The invention relates generally to the storage of data on magnetic recording tape, and more specifically, to the threading of a tape from a single reel tape cartridge through a curvilinear tape path to a take-up reel in a tape transport.
2. Related Art
The data processing industry stores large amounts of digital data on magnetic tapes. The 3480 tape cartridge (developed by IBM Corporation, Armonk, N.Y., U.S.A.) is an industry standard for magnetic storage media. The 3480 cartridge is a single reel cartridge with a length of 1/2 inch wide magnetic tape stored on it. The cartridge housing protects the tape from damage while allowing the tape reel to be driven from a drive mechanism on the underside of the cartridge housing. The tape is withdrawn from an opening formed at one corner of the cartridge. A leader block attached to a free end of the tape allows the tape to be withdrawn from the cartridge for read/write operations.
Read/write operations are performed by a tape "transport." The standard tape transport accepts the tape cartridge into an elevator assembly. A threading mechanism grabs the leader block and pulls it free from the cartridge. The threading mechanism pulls the leader block to thread the tape around a series of guide posts, across a longitudinal read/write head, and into a slot in a take-up reel. Once threaded, the tape from the cartridge can be driven across the read/write head for data transfer operations.
Data is currently stored on a 3480 cartridge in an 18 track longitudinal format. The tape path of the conventional transport for longitudinal recording is quite simple. The conventional threading mechanism is an arm which couples to the leader block and then pivots about a point of rotation to sweep the leader block through an arc. The arc traverses the read/write head and terminates at the take-up reel.
Storage Technology Corporation of Louisville, Colo., is currently developing a tape transport which will store data on a single reel cartridge in a helical storage format. The helical scan transport is detailed in commonly owned, copending U.S. patent appl. No. 08/060,653, filed May 13, 1993, which is incorporated herein by reference. The helical format results in storage densities more than one hundred times greater than that available using longitudinal recording techniques.
The helical scan transport is quite different from the longitudinal transport. The helical scan transport includes a cylindrical rotating head around which the tape must be wrapped for read/write operations. The helical scan tape path is much more complex than the path for a longitudinal transport. As a result, the simple pivot arm tape threading mechanisms used in longitudinal drives may not be suitable for use in a helical scan transport.
For example, the form factor of the helical scan transport of the '653 application requires that the take-up reel and the tape cartridge be disposed at opposite sides of the helical head in a substantially linear arrangement. The resulting path through which the tape must be threaded is curvilinear (i.e., substantially linear but including curves through which the tape must be navigated).
To thread a tape through such a curvilinear tape path, a raised linear threading mechanism has been developed. The raised linear threading mechanism is detailed in commonly owned, U.S. pat. appl. No. 08/060,663, filed on May 13, 1993, now U.S. Pat. No. 5,333,810, which is also incorporated herein by reference.
It is desirable to minimize the time required to thread a tape through the curvilinear tape path. However, if the tape is carried too quickly through the path, the tape and/or the trailing end of the leader block may collide with components of the transport. The present invention is directed to optimizing (i.e., minimizing thread time and stress on the tape while preventing leader block collisions) the threading operation.